The present invention relates to electronic information storage. More specifically, the invention relates to the storage of electronic information on non-volatile sequential media.
Tape media and other sequential storage media provide storage for important information. However, due to the technology used in recording information on the sequential storage media, overwriting specific portions of already recorded information is not permitted. As a result, a piece of tape media may contain obsolete data along with current data, and over time, the obsolete data may occupy a significant part of the media. The storage space dedicated to the obsolete data vastly increases the maintenance costs of the tape media storage. For instance, more pieces of tape media than necessary are required to store an entity""s data, which requires more tape media, increased physical storage locations, and additional mechanisms or manual intervention by administrators to access the additional tape media.
Until now, there has not been any manageable way to decrease the amount of tape media necessary for maintaining important information on the media.
The present invention provides a system and method for storing information to a sequential storage media such that storage space occupied by data deemed obsolete may be reclaimed. To that end, information is written to the storage media as sequential data sets with each data set including a catalog describing the information in the data set.
In accordance with one aspect of the invention, a new catalog type (a reclamation catalog) is provided that identifies the obsolete data stored on the media. The reclamation catalog may be written to the media periodically to identify data already stored on the media that has become obsolete. The reclamation catalog may be written to the media in association with a null data set if necessary to conform with storage conventions.
In accordance with another aspect of the invention, a reclamation process transfers data from the source media (e.g., the tape media that includes obsolete data) to a destination media (e.g., a blank tape) while excluding the obsolete data identified in the reclamation catalog. The reclamation process may read a catalog stored on the source media that describes the data stored on the source media. The reclamation process then modifies that catalog with the information stored in the reclamation catalog to create a unified catalog. The unified catalog identifies which of the data stored on the source media is to be copied to the destination media. The reclamation process then copies the data identified in the unified catalog to the destination media. In that manner, the destination media contains only valid data, and the source tape may be erased and reused.
In accordance with still another aspect of the invention, a generation number may be associated with the storage media that identifies whether a reclamation process has been performed with respect to the storage media. An application that maintains its own information describing data objects stored on the storage media may update its own information if the generation number stored on the storage media is inconsistent with its own information. For instance, the information maintained by the application may be associated with a generation number-of two (2). If the application determines that the storage media now includes a generation number of three (3), the application may update its own information to reflect that a reclamation has occurred. More specifically, the application may update its own information in accordance with a mapping catalog that maps data objects stored on the storage media to a location of the data objects as they were stored on the older generation of the storage media.